1. Field of the Invention
The present invention relates to a transmission electron microscope having an electron spectroscope that spectrally decomposes an electron beam based on the amount of energy of the electron beam.
2. Description of the Related Art
The sizes of processed silicon semiconductors, the sizes of processed magnetic devices and the like have become minute. Thus, a reduction in degradation of characteristics of devices and a reduction in reliability of the devices are critical issues. In recent years, a two-dimensional element analysis, a spectral analysis using (scanning) transmission electron microscopy ((S)TEM) and a spectral analysis using electron energy loss spectroscopy (EELS) have been required in order to analyze a defect of a nanometer-sized area of a semiconductor device, and find and solve the cause of the defect in a new process for developing a device and in a new process for mass production.
An electron energy loss spectrum is mainly classified into a zero loss spectrum, a plasmon loss spectrum, and a core loss spectrum. The zero loss spectrum is acquired when an electron beam passes through a sample and does not lose its energy. The plasmon loss spectrum is acquired by exciting an electron present in a valence band and reducing energy of the electron. The core loss spectrum is acquired by exciting a core electron and reducing the energy of the electron. In the core loss spectrum, a fine structure is observed in the vicinity of an absorption edge. The fine structure is called an energy loss near-edge structure (ELNES), and has information that includes the state of an electron present in a sample and the state of a chemical bond present in the sample. Since an energy loss value (the position of the absorption edge) varies depending on the element, a qualitative analysis can be carried out. Information related to coordination around a target element can be obtained based on a change (called chemical shift) in the energy loss value. Therefore, a simple state analysis can be carried out.
In a conventional technique, a scanning transmission electron microscope (that uses a scanning coil to scan a sample with a restricted electron beam) and an electron spectroscope (that is capable of spectrally decomposing an electron beam based on the amount of energy of the electron beam) are used to spectrally decompose an electron beam after the electron beam passes through a sample, and to continuously acquire electron energy loss spectra from multiple areas on the sample.
In the above method, however, an aberration of the electron energy loss spectra may occur, or the positions of the origins of the electron energy loss spectra may be different due to a drift of an acceleration voltage applied to the electron beam or due to a change in a magnetic field or in an electric field derived from a change in disturbance occurring around a device. It is, therefore, difficult to compare the shapes of energy loss near-edge structures observed in electron energy loss spectra and compare chemical shifts observed in electron energy loss spectra.
In a technique disclosed in JP-A-2000-113854, a two-dimensional position detection element having pixels measures an electron beam for a short time multiple times, and detects a pixel that indicates a spectrum (of the electron beam) having the maximum intensity based on values detected by the pixels in the multiple measurements. The two-dimensional position detection element then detects a pixel that indicates a spectrum (of the electron beam) having the maximum intensity based on values detected by the pixels in each of the measurements. Then, the two-dimensional position detection element is shifted to ensure that the positions of the pixels, each of which is indicative of the spectrum having the maximum intensity, match each other. In this case, the pixels whose positions match each other are identified as pixels indicative of the same energy value. Thus, a measurement can be carried out for a long time by summing the values detected in the measurements.
In each of techniques disclosed in JP-A-2002-157973 and in JP-A-2003-151478, an electron beam detector detects the peak of a spectrum of an electron beam, and detects a difference between the position of the peak and a standard position on the electron detector. An electron position controller, which controls the position of the electron beam incident on the electron detector, corrects the difference. In addition, while the electron position controller controls the correction of the amount of the change in the position of the peak of the spectrum and a spectrum measurement performed by the electron detector, the electron position controller measures an electron energy loss spectrum.
In the aforementioned techniques, electron energy loss spectra are not acquired simultaneously from multiple points. Thus, when electron energy loss spectra acquired from multiple points are compared, it is difficult to determine whether a shift of a spectrum is derived from a chemical shift (that occurs due to a difference between the states of chemical bonds) or from disturbance. In the techniques, a spectrum used to detect the amount of the change in the position of the peak of the spectrum and a spectrum to be analyzed cannot be necessarily acquired simultaneously. Thus, it is difficult to completely correct the amount of the change in the position of the peak of the spectrum.
JP-A-H10-302700 discloses that although a typical transmission electron microscope sets a focal point of an electron beam focused in the direction of an x axis on a plane and a focal point of the electron beam focused in the direction of a y axis on the same plane to acquire a transmission electron microscope image, a transmission electron microscope described in JP-A-H10-302700 sets a focal point of an electron beam focused in the direction of an x axis on a spectral plane and a focal point of the electron beam focused in the direction of a y axis on an image plane.
As a result, an electron energy loss spectrum acquired from a portion (extending in the direction of the y axis) of the sample can be separated and observed. That is, an image (spectral image) including the spectrum has a stripe pattern corresponding to each laminated layer observed in a transmission electron microscope image shown in FIG. 2A. The image is acquired by an image detector and can be observed as a spectral image with an x axis representing the amount of an energy loss and a y axis representing positional information on the sample, as shown in FIG. 2B. Thus, it is possible to simultaneously observe electron energy loss spectra acquired from different portions of the sample. It is also possible to compare energy loss near-edge structures observed in electron energy loss spectra acquired from different portions of the sample and compare chemical shifts in detail.
The spectral image (disclosed in JP-A-H10-302700) with the x axis representing the amount of the energy loss and with the y axis representing the positional information on the sample is a two-dimensional image. The spectral image disclosed in JP-A-H10-302700 is acquired by an image detector after a condition of a lens such as an electron spectroscope is adjusted and after a focal point of an electron beam focused in the direction of the x axis and a focal point of an electron beam focused in the direction of the y axis are set on different planes. It is therefore possible to simultaneously observe electron energy loss spectra acquired from points in areas (included in the sample and different from each other) that extend in the direction of the y axis.